HR: 11:50h
AN: G32A-07    [Abstracts]
TI: Coseismic Slip Distribution of the 2002 Mw7.9 Denali Fault Earthquake
AU: * Hreinsdottir, S
EM: sigrun@giseis.alaska.edu
AF: Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK 99775 United States
AU: Freymueller, J
EM: jeff@giseis.alaska.edu
AF: Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK 99775 United States
AU: Burgmann, R
EM: burgmann@seismo.berkeley.edu
AF: University of California, Berkeley, Department of Earth and Planetary Science, 307 McCone Hall, Berkeley, CA 94720 United States
AU: Mitchell, J
EM: mitchell@corecom.net
AF: Crazy Mountains Joint Venture, 2000 E. Dowling Road, Suite 6, Anchorage, AK 99507 United States
AB: We have estimated coseismic displacements for the 2002 Mw7.9 Denali Fault Earthquake at 232 GPS sites in Alaska and Canada, 180 of them within one rupture length of the earthquake. The displacement field shows a typical right-lateral deformation pattern for an E-W trending fault that cuts the surface. In general sites SW and NE of the fault move away from the fault and subside, but sites NW and SE of the fault move toward the fault and rise. Displacements along a N-S profile, crossing the fault along the Trans-Alaska Pipeline, indicate right-lateral slip on a near vertical fault with a significant component of vertical motion, north side up. These observations are in agreement with typical geological surface offset measurements along the Denali Fault (Haeussler et al., in press 2004). We estimated slip on a 3D fault model using a bounded variable least squares inversion, allowing only right-lateral strike slip and north-side-up dip slip. Allowing for oblique slip along the Denali and Totschunda faults improves the model fit to the GPS data by about 30%. We see mostly right lateral strike-slip motion on the Denali and Totschunda fault but in few areas we see a significant component of dip slip. The slip model shows increasing slip from west to east along the Denali Fault, with a few higher-slip patches. We infer maximum slip (9-12 m) about 40 km west of the Denali-Totschunda junction. This coincides with where geological observations estimated maximum slip of 8.8 m. Slip of 1-3 m was estimated along the Totschunda fault with majority of the slip being at shallower than 9 km depth. We have limited resolution on the Susitna Glacier fault but the estimated slip along the fault is consistent with a Mw7.2 sub-thrust-event. Total moment release in the Denali earthquake is Mw7.90, assuming a rigidity of 30 GPa. The estimated slip distribution along the surface is in very good agreement with geological surface offset measurements not measured on glaciers, but we find that surface offsets measured on glaciers are biased to lower values. We use the geological surface data, ignoring data from glaciers, to further constrain slip at the surface. This additional data set gives us important information on slip on shallower portions of the fault where we lack near field GPS data. The resulting slip model gives a similar but more refined slip distribution, with Mw7.89.
DE: 7215 Earthquake parameters
DE: 1206 Crustal movements--interplate (8155)
DE: 1208 Crustal movements--intraplate (8110)
DE: 1242 Seismic deformations (7205)
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting